East Coast Braces for Hurricane Florence

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Posted: Wednesday, September 12, 2018 2:13 pm

According to a National Weather Service advisory, as of 5 p.m. Eastern Time Wednesday, Hurricane Florence was weakening slightly, but even if that continues, the huge cyclone is expected to deliver life-threatening storm surges and catastrophic flooding throughout the Carolinas and the southern and central Appalachians late this week into early next week.

While the hurricane hasn't strengthened in terms of peak winds, the inner-core and outer wind fields have continued to expand, resulting in an increase in the cyclone's total energy, which will create a significant storm surge event. The upper-level outflow remains impressive and is still expanding except toward the south.

Florence is moving toward the northwest and new global and regional models have come into much better agreement on Florence moving steadily northwestward around a strong ridge located between Bermuda and the U.S. mid-Atlantic region for the next 48 hours or so. By late on day 2, Florence is forecast to approach the southern portion of the North Carolina coast, then slow down considerably and turn westward within collapsing steering flow, with a very slow westward motion near the coasts of North and South Carolina continuing into Friday and Saturday.

Corrected-consensus models remain very close to each other and still shows Florence moving slowly westward across South Carolina and western North Carolina on day 4, followed by a slow northward motion up the Appalachian mountain chain on day 5.

A narrow window of opportunity remains during the next 24 hours or so for Florence to strengthen a little when the hurricane passes over the warmer SSTs and deeper warm water/higher upper-ocean heat content associated with the Gulf Stream, and low vertical shear conditions of 5-10 kt will aid in any strengthening process.

However, significant strengthening is not anticipated due to Florence's large and expanding inner-core wind field. By 36 hours and beyond, decreasing ocean heat content along with the slowing forward speed of Florence will likely produce cold upwelling beneath the hurricane, inducing a gradual weakening trend. When Florence moves over the shallow coastal shelf waters in 48-72 hours, land interaction and more significant upwelling are anticipated, which should further enhance the weakening process. The National Hurricane Center's intensity forecast remains near the higher statistical guidance through 48 hours, then follows the trend of the decay SHIPS model after that time.

Although the maximum winds are expected to weaken a little more, Florence is still expected to remain a dangerous major hurricane as it approaches the coast. The threat to life from storm surge and rainfall will not diminish, and these impacts will cover a large area regardless of exactly where the center of Florence moves.

Key Messages:

1. A life-threatening storm surge is now highly likely along portions of the coastlines of South Carolina and North Carolina, and a Storm Surge Warning is in effect for a portion of this area. All interests in these areas should complete preparations and follow any advice given by local officials.

2. Life-threatening, catastrophic flash flooding and prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians late this week into early next week, as Florence is expected to slow down as it approaches the coast and moves inland.

3. Damaging hurricane-force winds are likely along portions of the coasts of South Carolina and North Carolina, and a Hurricane Warning is in effect. Strong winds could also spread inland into portions of the Carolinas.

4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents.

For specific local information, go to the website of the National Weather Service - www.weather.gov. Get the latest complete advisory issued by the National Hurricane Center at www.hurricanes.gov.

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